The key fundamental weakness (the susceptibility to man-in-the-middle attacks) was addressed in the original BB84 publication [1]: The need for the public (non

The key fundamental weakness (the susceptibility to man-in-the-middle attacks) was addressed in the original BB84 publication [1]: The need for the public (non-quantum) channel in this scheme to be immune to active eavesdropping can be relaxed if the Alex and Bob have agreed beforehand on a small secret key, which they use to create Wegman-Carter multiple-message authentication tags for their messages over the public channel. Of course immediately raises the question why one should use QKD at all. If a shared secret is required anyway, why not simply use symmetric cryptography? In many modern articles, QKD is presented as a replacement for asymmetric cryptography. This I think is very misleading, since the reason for using asymmetric cryptography is that one does not need a shared secret. [1] http://researcher.watson.ibm.com/researcher/files/us-bennetc/BB84highest.pdf http://researcher.watson.ibm.com/researcher/files/us-bennetc...